Selective separation of pyrene from mixed polycyclic aromatic hydrocarbons by a hexahedral metal-organic cage

Abstract

Polycyclic aromatic hydrocarbons (PAHs) play an important role in the industry, and the development of new materials for the selective separation of PAHs is of great significance. In this work, we report a hexahedral metal-organic cage with low symmetry by subcomponent self-assembly. In this cage, the eight ZnII centers adopt an interesting ΛΛ/ΔΔΔΔΔΔ or ΛΛΛΛΛΛ/ΔΔ configuration. This cage with a cavity volume of 520 Å3 can bind anthracene, phenanthrene, and pyrene to form 1:1 host-guest complexes, while the bigger triphenylene, chrysene, perylene, and coronene cannot be encapsulated. The binding constant Ka of pyrene is about 1.110 × 103 (mol/L)−1, which is more than an order of magnitude larger than that of anthracene and phenanthrene (111 (mol/L)−1, 277 (mol/L)−1, respectively). X-ray structure studies reveal that the pyrene is located in the cavity and stabilized by multiple CH⋅⋅⋅π interactions. After separation from a mixture of PAHs, pyrene with >96.1% purity can be obtained. This work provides a useful method for the first time for the selective separation of pyrene from PAHs mixture by utilizing a metal-organic cage as the material, making it a useful tool for purifying and separating specific compounds from complex mixtures.